Catheters, particularly intravenous (IV) catheters, are used for infusing fluid, such as normal saline solution, various medicaments and total parenteral nutrition, into a patient or withdrawing blood from a patient. Peripheral IV catheters tend to be relatively short, and are on the order of about one and one-half inches in length. The most common type of IV catheter is an over-the-needle peripheral IV catheter. As its name implies, an over-the-needle catheter is mounted over an introducer needle having a sharp distal tip. The catheter and the introducer needle are assembled so that the distal tip of the introducer needle extends beyond the distal tip of the catheter with the bevel of the needle facing up away from the patient's skin.
The catheter and introducer needle assembly is inserted at a shallow angle through the patient's skin into a peripheral blood vessel, i.e., a smaller blood vessel that is not connected directly to the heart but is one of the branches of the central blood vessels that is directly connected to the heart. In order to verify proper placement of the assembly in the blood vessel, the clinician confirms that there is flashback of blood in the needle and in a flashback chamber located at the proximal end of the needle, which is typically formed as part of the needle hub. Once proper placement is confirmed, the clinician applies pressure to the blood vessel by pressing down on the patient's skin over the distal tip of the introducer needle and the catheter. This finger pressure occludes further blood flow through the introducer needle. The clinician withdraws the introducer needle, leaving the catheter in place, and attaches a fluid-handling device to the catheter hub. Once the introducer needle is withdrawn from the catheter, it is a “blood contaminated sharp” and must be properly handled.
In recent years, there has been great concern over the contamination of clinicians with a patient's blood and a recognition that “blood contaminated sharps” must be immediately disposed. This concern has arisen because of the advent of currently incurable and fatal diseases, such as Acquired Immunosuppressive Deficiency Syndrome (“AIDS”), which can be transmitted by the exchange of body fluids from an infected person to another person. Thus, contact with the body fluid of an HIV-infected person should be avoided. As noted above, if an introducer needle has been used to place a catheter in the vein of an HIV-infected person, the introducer needle may be a vehicle for the transmission of the disease. Although clinicians are aware of the need to properly handle “blood contaminated sharps,” in certain medical environments, such as emergency situations or as a result of inattention or neglect, needle sticks from contaminated introducer needles may occur.
As a result of the problem of accidental needle sticks by “blood contaminated sharps,” various needle shields have been developed. Examples of such shields are disclosed in U.S. Pat. No. 6,004,294 and U.S. patent application Ser. No. 09/717,148 (filed Nov. 21, 2000), both incorporated herein by reference. These shields operate by engaging a feature, such as an enlarged diameter portion, formed on the needle. The engaging means may take many forms, such as a spring gate biased to contact the enlarged diameter portion of the needle when the tip of the needle is within the shield. Due to the small size of the needle and its delicate structure, it has been difficult to provide a feature that can withstand adequate force without affecting the operation of the needle itself. Further, such features have traditionally included a ramp, a radius or angled surface extending from the surface of the needle that may create difficulty in capturing the tip within the shield or may result in exertion of force on the needle in a non-axial direction.